Messier 97, 108 & NGC 3631 — Wide Field
Key Scientific Data
Main objects: M97 (Owl Nebula), M108 (Surfboard Galaxy), NGC 3631
Constellation: Ursa Major
M97: Planetary nebula
M108: Spiral galaxy
NGC 3631: Spiral galaxy
M97 distance: approximately 2,000 light-years
M108 distance: approximately 45–50 million light-years
NGC 3631 distance: approximately 50 million light-years
M97 apparent magnitude: approximately 9.9
M108 apparent magnitude: approximately 10.0
NGC 3631 apparent magnitude: approximately 10.4
M97 other designations: Messier 97, NGC 3587, Owl Nebula
M108 other designations: Messier 108, NGC 3556, Surfboard Galaxy
NGC 3631 other designation: PGC 34767
Description
This wide-field image of Ursa Major brings together three remarkably different astronomical objects: the planetary nebula Messier 97, the edge-on spiral galaxy Messier 108, and the face-on spiral galaxy NGC 3631.
Although they appear within the same photographic field, they have virtually no physical relationship with one another.
M97 belongs to our own Milky Way and lies only a few thousand light-years away. M108 and NGC 3631, by contrast, are entire galaxies located tens of millions of light-years beyond the Milky Way.
The image therefore contains an extraordinary range of astronomical scales, from the remains of a single dying star to galaxies containing billions of stars.
Why Broadband Imaging?
M97 is primarily an emission nebula, and broadband RGB imaging is therefore not the most efficient way to reveal its faint structure. Narrowband filters, particularly OIII and H-alpha, are much better suited to isolating the emission from the nebular gas and revealing the subtle details of the Owl Nebula.
In this case, however, the purpose of the image was deliberately different.
The use of broadband RGB filters was chosen to capture a much wider astronomical scene including not only M97, but also the galaxies M108 and NGC 3631, together with the numerous much fainter galaxies scattered throughout the background.
Narrowband imaging would strongly suppress the continuum light emitted by these galaxies, making it unsuitable for the main objective of this wide-field composition.
The result is therefore a compromise by design: less emphasis on the faint nebular structures of M97, but a much richer representation of the surrounding extragalactic field, while preserving the natural colours of the stars and galaxies.
In this image, M97 is not intended to be observed in isolation, but as part of a much larger cosmic landscape extending from a planetary nebula within our own Milky Way to galaxies tens of millions of light-years away.
The Owl Nebula — M97
Messier 97, better known as the Owl Nebula, is one of the most famous planetary nebulae in the northern sky.
It represents a relatively brief final stage in the evolution of a star broadly similar in mass to the Sun.
After exhausting the nuclear fuel available in its core, the progenitor star expanded and eventually expelled its outer layers into space. The extremely hot stellar remnant left behind ionises this expanding material with ultraviolet radiation, causing the surrounding nebula to glow.
The characteristic appearance of M97 is dominated by two darker regions within its approximately circular shell. Visually, these resemble the large dark eyes of an owl, giving the nebula its familiar nickname.
At the centre lies the hot remnant of the original star, evolving toward the white-dwarf stage.
M108 — The Surfboard Galaxy
On the opposite side of the field lies Messier 108, commonly known as the Surfboard Galaxy.
Unlike M97, M108 is not part of our immediate stellar neighbourhood. It is an entire spiral galaxy seen almost edge-on from Earth and located approximately 45–50 million light-years away.
Its highly inclined orientation gives it the elongated appearance responsible for its nickname.
Dark dust lanes cross the galactic disk, while numerous regions of active star formation are distributed throughout its irregular-looking structure. Because we observe the galaxy almost from the side, its spiral pattern is much less obvious than in galaxies viewed face-on.
The contrast between M97 and M108 is particularly striking: one is the expelled atmosphere of a single dying star within our Galaxy, while the other is itself an enormous system of stars, gas and dust millions of light-years away.
NGC 3631 — A Face-on Spiral
The third prominent deep-sky object in this field is NGC 3631, a spiral galaxy seen much more nearly face-on.
Its orientation provides a very different perspective from M108. Instead of an elongated galactic disk, we see the spiral structure opening outward around the central region.
Its arms contain numerous concentrations of young stars and star-forming regions, producing the characteristic fragmented appearance visible in deep astronomical images.
NGC 3631 lies roughly 50 million light-years from Earth, meaning that the light recorded in this image began its journey long before humans existed.
Three Objects, Three Different Perspectives
One of the most interesting aspects of this field is the contrast between the three principal objects.
M97 shows us the final evolutionary stages of an individual star.
M108 shows an entire spiral galaxy almost edge-on.
NGC 3631 presents another spiral galaxy from a much more face-on perspective.
Their apparent proximity is purely a consequence of perspective. M97 is located within the Milky Way, whereas the two galaxies lie millions of times farther away.
A wide-field photograph therefore transforms what appears to be a single region of sky into a remarkable demonstration of the enormous three-dimensional depth of the Universe.
A Field Full of Galaxies
M97, M108 and NGC 3631 are only the most conspicuous objects in the photograph.
The deep RGB exposure reveals numerous much smaller and fainter galaxies scattered throughout the background. Many appear only as tiny elongated smudges or faint reddish structures between the foreground stars of the Milky Way.
Each is a separate stellar system lying far beyond our Galaxy.
The annotated version of the field makes this particularly evident: what initially appears to be largely empty space is populated by a remarkable number of catalogued galaxies, many identified by their PGC designations.
The wide field therefore extends far beyond the three principal objects and provides a glimpse into the large-scale population of galaxies in this direction of the sky.
Looking Back in Time
This photograph simultaneously records light from dramatically different epochs.
The light from M97 has travelled for only a few thousand years before reaching Earth.
The photons from M108 and NGC 3631, however, have travelled for approximately 50 million years.
When that galactic light began its journey toward us, Earth was in the Eocene Epoch. Mammals were undergoing major evolutionary diversification, and human beings would not appear for tens of millions of years.
For all that time, those photons crossed intergalactic space before finally reaching the telescope and sensor used to create this image.
The photograph therefore does not show the three objects at the same moment in cosmic history.
Within a single frame, we are simultaneously looking a few thousand years and tens of millions of years into the past.
Image Data
Total integration time: 4h 6m
Integration by filter:
-
Red: 1h 54m (38 × 180")
-
Green: 1h 12m (24 × 180")
-
Blue: 1h (20 × 180")
Equipment:
-
Telescope: William Optics RedCat / Cat 51 III WIFD
-
Camera: ToupTek ATR2600M
-
Mount: 10Micron GM2000 HPS II
-
Filters: Optolong Blue 2", Optolong Green 2", Optolong Red 2"
-
Accessories: ToupTek AAF Electric Focuser, WandererAstro WandererCover V4-EC
-
Software: Adobe Photoshop, Pleiades Astrophoto PixInsight, Stefan Berg Nighttime Imaging 'N' Astronomy (N.I.N.A. / NINA)
For further information and the full-resolution image, visit AstroBin: